Summary of work: The major scientific accomplishments during the past year include publication of important research findings related to the effects of calorie restriction (CR) in monkeys on parameters related to human diseases of aging. For example, we reported that serum DHEAS, which declines markedly during human aging and has been implicated in a number of diseases, also declined in aging rhesus monkeys. Most importantly, the rate of decline in serum DHEAS was slowed in adult monkeys on CR. This suggests that CR might slow post-maturational aging, at least as indexed by this serum marker, in primates. Another important finding was that rhesus monkeys on CR exhibited higher serum levels of certain HDL cholesterol subfractions. Low levels of these particular HDL subfractions have been associated with increased risk of cardiovascular disease in humans. These findings combined with data showing beneficial effects of CR on blood pressure, triglycerides, and cholesterol suggest that t his paradigm lowers the risk of cardiovascular disease. We plan to continue investigating the effects of CR on cardiovascular disease in two major areas. First, we are beginning a retrospective study of the effects of CR on "Syndrome X" the metabolic cardiovascular syndrome. Several of the components of Syndrome X, such as body composition and insulin responsiveness, have been shown previously to be affected positively by CR. In addition, we have begun a new collaborative effort with the Cardiovascular Laboratory at the GRC to investigate the effects of aging and CR on measures of arterial stiffness in our monkeys. Osteoporosis is another age-related disease under investigation in the laboratory. Recently completed studies have shown those skeletal changes seen in rhesus monkeys during aging are similar to that reported in humans. Both premenopausal females and older male monkeys exhibit a slight (<1%) loss of bone with advancing age. The oldest female monkeys in our colony also have begun to experience menstrual irregularity and hormonal changes consistent with those reported in humans entering menopause. In premenopausal females CR does not result in a significant global loss of bone. Instead, CR monkeys exhibit a light, selective, and none significant loss of bone at some skeletal sites. Biochemical studies of bone turnover and other bone metabolic hormones suggest that CR does not have detrimental effects on these parameters. As such, it is likely that the observed differences between control and CR mon keys are due to altered biomechanical stresses related to differences in body composition. Further directions for this line of research include in depth study of the female monkeys as they enter menopause. In the past year we have begun a major effort to investigate possible metabolic mechanisms of CR. This effort includes several short-term monkey studies related to metabolic adaptation to changes (both restriction and refeeding) in intake level. In addition to our previous findings of a reduced body temperature during short-term CR, we have shown that fasting insulin, but not glucose levels appear to be regulated by acute changes in food intake level. In the coming year several studies using this short-term paradigm are planned. For example, in association with various collaborators we plan to investigate the effects of short-term CR on mitochondrial metabolism, oxidative stress and transcriptional regulation of chaperone proteins. Tissue biopsies have already been completed on several cohorts of monkeys and several groups will complete the study by the end of this year.